The invention relates generally to network communications. More specifically, the invention relates to methods and systems that find diverse optical routes in multi-vendor networks with minimum total cost or minimal total distance.
With technology evolution and industry consolidation, a large carrier's core transport network may include several Dense Wavelength Division Multiplexer (DWDM) systems from different vendors using different technologies. A traditional point-to-point (unidirectional) DWDM system would employ one optical multiplexer, an optical fiber and one optical demultiplexer. The optical multiplexer can combine n wavelength signals together and transmit the multiplexed signal over the fiber to the demultiplexer. The demultiplexer decomposes the multiplexed signal back into n wavelength signals. Two electronic devices, such as routers, may be connected over a single wavelength.
FIG. 1 shows an exemplary point-to-point DWDM system 101 that comprises forwarding client routers 1031, 1032, . . . 103n (collectively 103) a forwarding terminal Optical Transponder (OT) 105, an optical multiplexer 107, an optical fiber 109, an optical demultiplexer 111, a receiving terminal OT 113 and receiving client routers 1151, 1152, . . . 115n (collectively 115). A forwarding router 103 transmits a client signal with a common short-reach wavelength λ0. Before entering the optical multiplexer 107, the signal is converted into another wavelength λ1 via the forwarding terminal OT 105. The λ1 signal is combined with other wavelength signals λ2, . . . , λn and transmitted over the fiber 109 to the demultiplexer 111. The demultiplexer 111 decomposes the combined signal λ1, λ2, . . . , λn back to their separate wavelengths. The λ1 signal is converted into the common short-reach wavelength λ0 by the receiving terminal OT 113 and the wavelength λ0 may be received by a receiving client router 115.
A bidirectional DWDM communications system comprises two fibers—one fiber for each communication direction. The signal transmission of the return direction is similar. When a connection is switched from one DWDM system to another DWDM system, two OTs are needed. The first OT converts the first DWDM system wavelength into a common short-reach wavelength (λ0) and the second OT converts the common short-reach wavelength (λ0) into a second DWDM system wavelength.
However, when the two DWDM systems are of the same technology from the same vendor, one optical regenerator OT can be used to replace two back-to-back terminal OTs and avoid the conversion to an intermediate, common short-reach wavelength thereby reducing component cost. An optical regenerator OT is less expensive than two terminal OTs.
Reconfigurable Optical Add-Drop Multiplexer (ROADM) technologies for DWDM transports are being deployed due to their high capacity and capital savings. A ROADM network typically includes a set of multi-degree nodes connected via fibers to form a mesh topology. Traffic may be added or dropped, or expressed at ROADM nodes.
ROADMs are a form of optical add-drop multiplexer that adds the ability to remotely switch traffic from a DWDM system at the wavelength layer. This allows individual wavelengths carrying data channels to be added and dropped from a transport fiber without the need to convert the signals on all of the WDM channels to electronic signals, and back again to optical signals. The main advantages of ROADMs are the planning of the entire bandwidth assignment need not be carried out during initial deployment of a communications system, the configuration may be performed as and when required. ROADMs allow for remote configuration and reconfiguration.
From the perspective of the switch fabric, the terminal used to add and drop channels is that of a transmit/receive port. It employs tunable lasers and filters that allow any wavelength at a terminal/switch fabric interface to be routed to any terminal transmit/receive port. It also contains regenerator OTs that can perform wavelength translation.
Using ROADM systems, a wavelength connection or lightpath is able to travel a long distance such as 1500 km or more without requiring Optical to Electronic to Optical (OEO) regeneration. This distance limit is referred to as the optical-reach. A regenerator OT is needed when a connection length is longer than the optical-reach. An optical path without regeneration is called an express link.
Today, most ROADM based systems support OC-192 (10 Gbps) or OC-768 (40 Gbps) per wavelength. But a large portion of connections are still provisioned using lower speeds such as OC-48 (2.5 Gbps). A network carrier needs to be able to multiplex low speed connections into a high speed wavelength lightpath in a ROADM network where each low speed connection occupies one subchannel of the wavelength lightpath. For example, one OC-192 may comprise four OC-48 subchannels. A high speed wavelength lightpath with multiplexing capability is called a multiplex link.
In DWDM systems, optical signals are transmitted over fibers. Multiple fibers are combined together and deployed over a common conduit. The fiber conduits form a fiber map. In the fiber map, fiber nodes are ROADM sites and fiber joints, where fiber joints are fiber branch locations. Fiber segments between two neighbor fiber nodes are called fiber spans. DWDM systems are built upon fiber spans. In DWDM systems, the traffic add/drop/express through sites are called DWDM nodes, and fiber span connections between two DWDM nodes are called DWDM links. Multiple DWDM links may share the same fiber span, which are labeled a Shared Risk Link Group (SRLG) since a fiber span cut can affect all the DWDM links in the group.
In summary, optical networks can be decomposed into four layers: 1) a fiber span layer, 2) a DWDM link layer, 3) an express link layer and 4) a multiplexing link layer.
Network planners are often requested to provision multiple physically diverse optical routes with different source, different destination and different bandwidth requirements. For example, an enterprise customer may ask for an optical Virtual Private Network (VPN) connecting multiple operation sites, and that the optical VPN routes are physically diverse from each other for high network availability.
Physical diversity means no sharing of fiber spans, fiber joints, and other optical facilities among each route. This problem becomes more complicated due to heterogeneous optical networks' multiple layers and heterogeneous vendor systems.
Finding two SRLG diverse routes between two DWDM nodes is already non-deterministic polynomial-time (NP) hard (i.e. possibly no existence of any fast polynomial-time solution method). Therefore to find multiple SRLG diverse routes plus additional engineering constraints like bypassing or including/excluding DWDM nodes in routes is also NP-hard.
Currently there is no existing tool to solve this complicated problem and network planners often rely on their experiences and spread sheets to find feasible solutions.
What is desired is a method and system that finds multiple diverse optical routes with minimum total cost or total distance in heterogeneous multi-layer multi-vendor optical networks.